1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a solid state image sensor and a method of manufacturing the same.
2. Description of the Related Art
Solid state image sensors are used in a variety of applications in disciplines such as public security, industry, broadcasting, and the military. For example, solid state image sensors are used in various devices such as cameras, camcorders, multimedia devices, and surveillance cameras. Particularly, as miniaturization and the number of pixels of solid state image sensors increase, the demand for efficient manufacture of low-cost solid state image sensors, especially those that include on-chip micro-lenses, also increases.
Sensitivity and manufacturing yield are very important details to consider when manufacturing a solid state image sensor. Therefore, micro-lenses are formed on the upper portion of a sensor to improve sensitivity. A light ray incident on the solid state image sensor passes through the micro-lens, which is installed for improving the light collection efficiency, and the light energy is collected by a photodiode. The light energy collected by the photodiode is converted into a signal charge, and the signal charge is transmitted to an output terminal by a transmission device such as a vertical transmission charge-coupled device (CCD) or a horizontal transmission CCD. The signal charge transmitted to the output terminal is output as an electrical signal corresponding to the amount of energy imparted by the incident photons.
FIG. 1 is a sectional view illustrating a solid state image sensor including conventional micro-lenses.
Referring to FIG. 1, micro-lenses 122 are formed on a flat protection layer 120. The micro-lenses 122 are generally formed of an organic substance including photoresist. Photoresist patterns are formed, and are then heat treated and flowed, thereby forming convex lenses having a proper radius of curvature. However, if the photoresist patterns are formed by a thermal flow in two-dimensions on a flat protection layer 120, the radius of curvature of the respective micro-lenses 122 can vary, due to variations in local surface energy over a large area. Also, when forming the micro-lenses 122, thermal energy is continuously applied. If the contact area between the micro-lenses and the protection layer is large, that is, the radius of curvature is large, some micro-lenses may be stuck to an adjacent micro-lens, while other micro-lenses may not be stuck to an adjacent micro-lens. The thickness of the photoresist in the overlapped portions of the micro-lenses stuck to each other may be different. A diffused reflection is caused by excessive overlapping of micro-lenses. Therefore, in the respective micro-lenses, a difference in sensitivity occurs due to a difference in transmitted light intensity, and uniformity in sensitivity is reduced. Therefore, there is an imposed manufacturing limit in the maximum radius of curvature of the micro-lens in order to secure an improvement in sensitivity and a uniformity of size of the micro-lenses.